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Results for “Nuclear Structure”
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Large-scale calculations of 𝛽-decay rates and implications for 𝑟-process nucleosynthesis
Nuclear 𝛽 decay is a key element of the astrophysical rapid neutron capture process (𝑟 process). In this work, we present state-of-the-art global 𝛽-decay calculations based on the quantified relativistic nuclear energy density functional theory and the deformed proton-neutron quasiparticle random-phase approximation. Our analysis considers contributions from allowed and first-forbidden transitions. We used two point-coupling functionals with carefully calibrated time-odd terms and isoscalar pairing strength. The new calculations display consistent results for both employed functionals, especially near the neutron drip line, suggesting slower 𝛽 decays past the 𝑁=126 neutron shell closure than in commonly used 𝛽-decay models. The new rates, along with the existing rates based on the recent nonrelativistic global calculations, are found to slow down the synthesis of heavy elements in the 𝑟 process and significantly reduce the contribution of neutron-induced fission.
Extraction of neutron-capture cross sections on 92 Zr using the charge-exchange Oslo method
The 93 Nb (𝑡, 3 He ) reaction at 115 MeV/nucleon was studied to demonstrate that nuclear level densities and 𝛾-ray strength functions can be extracted from charge-exchange reactions at intermediate energies using the Oslo technique. The matrix of excitation energy in 93 Zr, reconstructed from the (𝑡, 3 He ) reaction, versus the energy of 𝛾 rays emitted by the excited 93 Zr nuclei, was obtained in an experiment with the S800 Spectrograph operated in coincidence with the GRETINA 𝛾 -ray detector. The extracted level density and 𝛾 -ray strength function obtained by applying the Oslo method to this matrix were used to estimate the 92 Zr(𝑛,𝛾) 93 Zr cross section by combining the new results with other experimental data and theoretical calculations for 𝐸1 and 𝑀1 strength functions at higher energies. Good agreement with direct measurements of the 92 Zr(𝑛,𝛾) 93 Zr cross section was found. The contribution from the upbend in the extracted 𝛾-ray strength function was important to achieve the consistency, as the neutron-capture cross section without this contribution is significantly below the direct measurements otherwise. Since charge-exchange reactions at intermediate energies have long been used for extracting Gamow-Teller strengths, the successful demonstration of the charge-exchange Oslo method enables experiments in which (𝑛,𝛾) cross sections and Gamow-Teller strengths can be measured simultaneously, which is of benefit for astrophysical studies.
Isomeric states in the neutron-rich 𝑁 = 108 nuclei 178 Yb and 179 Lu
A multinucleon transfer reaction with a 136 Xe beam and a gold-backed 176 Yb target populated isomers in N = 108 178 Yb and 179 Lu. The single decay from the t 1/2 = 203(16) ns isomer in 178 Yb to the I π = 4 + level in the ground-state band suggests a I π = 4 − assignment, and multiquasiparticle calculations associate this state with the K π = 4 − , ν 2 (1/2[510], 9/2[624]) configuration. At least two isomers were observed in 179 Lu. One likely couples the K π = 4 − configuration found in 178 Yb to the 9/2[514] quasiproton orbital to form a K π = 17/2 + level (t 1/2 = 1.0(4) µs) which primarily decays into the rotational band based on the 9/2[514] state. A second isomer was observed to decay into this same band, but at higher energy and spin. Based on its feeding pattern, its similarity to an isomer found in 181 Ta, and a multiquasiparticle calculation, it is proposed to correspond to a K π = 29/2 − state based on the π9/2[514]ν 2 (9/2[624], 11/2[615]) configuration. As a result, an analysis of the reduced hindrance factors for negative-parity, two-quasineutron isomers in the rare-earth region is presented as well.
Tunable magnetic excitations in the honeycomb antiferromagnet (Co,Ni)TiO3
The solid solution of the honeycomb antiferromagnet (AFM) Co0.5Ni0.5TiO3 (CNTO) was synthesized by mixing a 1:1 molar ratio of CoTiO3 (CTO) and NiTiO3 (NTO). Powder neutron scattering was used to determine the structure and magnetic spectrum, where the nuclear and magnetic structures resemble those of the end members. The Néel temperature (T𝑁 = 27 ± 1 K), the ordered magnetic moment (M = 2.29 ± 0.03 𝜇𝐵 per magnetic ion), and lattice parameters are intermediate between those of the two. From inelastic neutron scattering, it is observed that the magnon density of states (MDOS) extends up to 13 meV, and the interaction can be described by an XXZ-type magnetic Hamiltonian. Above 15 meV, spin-orbit excitons (SOEs) are observed similarly to those in CTO, but with modified spin-orbit crystal-field splitting because of the substitution of Ni at Co sites, and the disorder induced by the Ni substitution modifies the spin-orbit crystal field. Thus, the magnetic dynamics of the CNTO cannot be described as a simple average of the two parent compounds.
Electromagnetic radii of light nuclei from variational Monte Carlo calculations
We present variational Monte Carlo calculations of charge and magnetic radii in 𝐴 ≤ 10 nuclei. The calculations are based on the Norfolk two- and three-nucleon interactions, and associated one- and two-nucleon electromagnetic charge and current operators derived up to next-to-next-to-next-to-leading order in the chiral expansion. The charge and magnetic radii are extracted from the respective form factors. We find that the charge radii are within 5% of the experimental values for the nuclei considered. For the magnetic radii, a comparison is available only with 3 H and 3 He electron scattering data that are affected by large error bars. We hope that our predictions foster an interest in precisely measuring magnetic radii of heavier systems.
Puzzling 𝐵(𝐸2;0 + → 2 + ) strength in the proton dripline nucleus 36 Ca
Recent measurements of the 𝐸2 transition rate from the ground state to the first 2 + excited state of the proton dripline nucleus 36 Ca show an unusual pattern when compared to its isotopic neighbor 38 Ca: despite having a higher 𝐸 𝑥 (2$^{+}_{1}$) excitation energy, the 𝐵(𝐸2;0$^{+}_{1}$ → 2$^{+}_{1}$) rate in 36 Ca is larger. The question that naturally arises is to what extent this observation can be attributed to the unbound character of the 2$^{+}_{1}$ state. To understand the influence of the continuum space on the low-energy properties of 36 Ca, we carried out Gamow shell model calculations that can account for the continuum coupling effects associated with the occupation of unbound 𝑓𝑝 shells. We found that in the threshold 2 + state, 36 Ca is spatially diffused, which impacts the observed 𝐵(𝐸2) trend.
Experimental study of 53 Cr via the (𝑑, 𝑝𝛾) reaction
Excited states in 53 Cr were studied via the 52 Cr (𝑑, 𝑝𝛾) reaction up to the neutron-separation threshold. Proton-𝛾 angular correlations and 𝛾 decay branching ratios were measured in particle-𝛾 coincidences between the Super-Enge Split-Pole Spectrograph (SE-SPS) and CeBr 3 Array (CeBrA) demonstrator of the John D. Fox Accelerator Laboratory at Florida State University. Previous spin-parity assignments from a (𝑑,𝑝) singles experiment at the SE-SPS are supported and 𝛾-ray transitions in 53 Cr are reported. We firmly assign higher-lying excited states to 53 Cr because overlapping excited states and contaminants could be identified better due to the complementary 𝛾-decay information. We also correct some of the previously reported excitation energies and present a reanalysis of previously measured 52 Cr (𝑑, 𝑝) 53 Cr angular distributions guided by the complementary 𝛾-ray information. Based on this reanalysis, the fragmentation of the neutron 2𝑝 3/2 , 2𝑝 1/2 , 1𝑓 5/2 , 1𝑔 9/2 , and 2𝑑 5/2 single-particle strengths is reassessed for 53 Cr. Here, a comparison to the corresponding strengths in 55 Fe is presented.
Structural dynamics modeling of spent nuclear fuel during hypothetical package drop events
The response of spent nuclear fuel (SNF) to hypothetical package drop events is of particular interest in the scope of spent fuel storage and transportation because of the mechanical shock encountered in such scenarios. Previous testing and modeling by the U.S. Department of Energy has demonstrated that the shock and vibration environment of normal shipping and handling conditions (excluding package drop events) is relatively benign and does not challenge the integrity of spent nuclear fuel. Cask drop events are worth considering because SNF packages are required to withstand free drops onto unyielding surfaces as part of their licensing basis. The acceleration experienced during drop events can be orders of magnitude higher, and thus more advanced models are needed to encompass potential nonlinear behavior of the fuel, such as spacer grid buckling and rod-to-rod impact. This work describes a number of finite element models developed to calculate the response of spent nuclear fuel to various hypothetical drop events that have been validated by package and fuel assembly drop tests conducted in the last decade. Sensitivity of the model response to factors such as package drop orientation, secondary impacts, and irradiated material properties as well as their potential impacts to fuel cladding integrity, was also investigated. Cask drops are not expected as a regular occurrence during SNF transportation, but this work helps raise the understanding of SNF mechanical loads to the point of consistency with the package design requirements.
Dispersive corrections in elastic electron-nucleus scattering: an investigation in the intermediate energy regime and their impact on the nuclear matter
Measurements of elastic electron scattering data within the past decade have highlighted two-photon exchange contributions as a necessary ingredient in theoretical calculations to precisely evaluate hydrogen elastic scattering cross sections. This correction can modify the cross section at the few percent level. In contrast, dispersive effects can cause significantly larger changes from the Born approximation. The purpose of this experiment is to extract the carbon-12 elastic cross section around the first diffraction minimum, where the Born term contributions to the cross section are small to maximize the sensitivity to dispersive effects. The analysis uses the LEDEX data from the high resolution Jefferson Lab Hall A spectrometers to extract the cross sections near the first diffraction minimum of 12 C at beam energies of 362 MeV and 685 MeV. The results are in very good agreement with previous world data, although with less precision. The average deviation from a static nuclear charge distribution expected from linear and quadratic fits indicate a 30.6% contribution of dispersive effects to the cross section at 1 GeV. The magnitude of the dispersive effects near the first diffraction minimum of 12 C has been confirmed to be large with a strong energy dependence and could account for a large fraction of the magnitude for the observed quenching of the longitudinal nuclear response. These effects could also be important for nuclei radii extracted from parity-violating asymmetries measured near a diffraction minimum.
The $^3$He+$^5$He$\rightarrow $ $\alpha $+$\alpha $ reaction below the Coulomb barrier via the Trojan Horse Method
For the first time in an application to nuclear astrophysics, a process induced by the unstable 5 He = ( 4 He-n) nucleus, the 3 He+ 5 He→2α reaction, has been studied through the Trojan Horse Method (THM). For that purpose, the quasi-free (QF) contribution of the 9 Be( 3 He,αα) 4 He reaction was selected at E 3 He =4 MeV incident energy. The reaction was studied in a kinematically complete experiment following a recent publication, where for the quasi free contribution the momentum distribution between α and 5 He particle cluster in the 9 Be nucleus in the ground state have been extracted. The angular distribution of the QF 3 He+ 5 He→2α reaction was measured at θ cm = 78°–115°. The energy dependence of the differential cross section of the 3 He+ 5 He→2α virtual reaction was extracted in the energy range E cm = 0–650 keV. In conclusion, the total cross section obtained from the Trojan-horse method was normalized to absolute cross sections from a theoretical calculation in the energy range E cm =300–620 keV.
Medium-spin states in $^{116,118,120,122,124}$In
Here, the $^{116,118,120,122,124}$In nuclei have been populated as fission fragments in reactions induced by heavy ions. Level schemes have been built from γ-rays detected using the Gammasphere array. Medium-spin states of $^{118,120}$In 69,71 nuclei have been identified for the first time, while the level schemes of $^{116,122,124}$In 67,73,75 were enriched. The observed states at lower excitations and at medium spin can be described by the coupling of the proton g 9/2 hole to the neutron or neutron-hole in the h 11/2 orbital. This coupling can now be followed in all odd-odd In isotopes from $^{104}$In 55 to $^{126}$In 77 .
Data for "Integrated Green Biorefinery for the Production of Anthocyanins, Fermentable Sugars, and High Pure Lignin from Miscanthus × giganteus "
Miscanthus x giganteus (Mxg) is a promising perennial crop for producing natural colorants, renewable fuels, and bioproducts. However, natural recalcitrance and high pretreatment cost are major barriers to their complete conversion. In this study, a green processing method has been investigated for efficient recovery of natural pigments (anthocyanins), fermentable sugars, and pure lignin from Mxg genotypes using choline chloride-based natural deep eutectic solvents (NADES) systems. Interestingly, choline chloride: lactic acid (ChCl: LA) NADES-processed biomass resulted in 67.8 ± 2.1 μg g−1 of anthocyanins from dry biomass. A maximum of 87.4%–94.1% glucose yield was achieved after enzymatic saccharification. The effective extraction of lignin with high purity with higher β-aryl ether (βO4) bonds from advanced crops is crucial for lignin valorization. Notably, highly pure lignin (≈93.4% ± 1.4%) is achieved after low-temperature NADES pretreatment while retaining lignin’s native structure. 31P nuclear magnetic resonance demonstrated that total phenolics for ChCl: LA-lignin resulted in 1.20 mmol g−1 hydroxyls. The relative monolignol composition of syringyl (S), guaiacyl (G), and p-hydroxyphenyl (H) is 19.0, 65.7, and 14.3%, respectively, as evidenced by heteronuclear single quantum coherence analysis. This study provides a novel approach for obtaining high-purity lignin for catalytic depolymerization for oligomers and bifunctional monoaromatics production and leverages current cellulosic biorefinery technologies.
Nuclear Wallet Cards
The Nuclear Wallet Cards present properties for ground and isomeric states of all known nuclides. It provides the following: Spin and parity assignments, Nuclear mass excesses, Half-lives, isotopic abundances, Decay modes. Appendices contain properties of elements, fundamental constants and other useful information.
Update on activities in the NEA Nuclear Science Committee relevant to the NCSP [Slides]
Abstract not provided.
Fragmentation and Space-Time Reciprocity [Slides]
Through fragmentation processes and high energy collisions we access the internal structure of nuclear matter in terms of quarks and gluons, create new states of nuclear matter, and understand the transition from quarks and gluons to hadrons.
Status of GNDS support in AMPX [Slides]
This presentation provides an overview of ENDF reading in AMPX, as well as information regarding low level access classes for GNDS used in AMPX and the use of these classes in AMPX and SAMMY.
Status of FUDGE [Slides]
This presentation discusses the nuclear data management code FUDGE (For Updating Data and Generating Evaluations). While FUDGE is designed to support GNDS, the presentation also states that ENDF-6 and ENDL data files are also supported but must first be translated into GNDS; translators are included with FUDGE. It also states that FUDGE supports plotting, manipulating, checking for physical content, resonance reconstruction, Doppler broadening, etc. FUDGE also supports processing for Monte Carlo and deterministic transport. FUDGE is open source, and the latest public release was FUDGE-4.2.3 with support for GNDS-1.9. In summation, FUDGE capabilities include translating older formats into GNDS, translating GNDS back to ENDF-6, and visualizing, modifying, checking, and processing GNDS data. It also states that a new version of FUDGE is coming soon. The plan is to support GNDS-2.0 specification, but it may be released sooner if v2.0 is delayed.